(1) Field of the Invention
The present invention relates to a method and apparatus for cleaning of the harmful gas discharged from a reaction process using an organic metal compound as a reaction raw material, and, particularly, to a method and apparatus for cleaning of the harmful gas discharged from an MOCVD (Metal Organic Chemical Vapor Deposition) process, other CVD processes or the like in semiconductor-manufacturing processes.
(2) Description of the Prior Art
Materials constituting an insulated thin film of a semiconductor device include SiO2 for a gate insulated film, Si3N4 for a capacitor insulated film, PSG (phosphorous/silicon/glass) and BPSG (boron/phosphorous/silicon/glass) for a layer insulated film and the like. Gaseous raw materials such as SiH4, NH3, PH3 and B2H6 have been used as materials for producing these films in CVD apparatus. With progresses in three-dimensional devices and multilayer interconnection, there is an increased demand for flattening of an insulated film. The adoption of CVD processes using, as starting material, a liquid organic metal compound is going to start, the liquid organic metal compound including tetraethoxysilane (Si(OC2H5)4), trimethoxyboron (B(OCH3)3) and trimethoxyphosphorous (P(OCH3)3) which are resistant to failures such as voids and enables the formation of high quality thin film. In addition, new types of thin film such as a Ta2O5 film having a dielectric constant several times that of SiO2 have been developed. As the raw material of the Ta2O5 film, pentaethoxytantalum (Ta(OC2H5)5) which is a liquid organic metal material is used.
Moreover, in recent years, as oxide type dielectric thin films for semiconductor memories, a lead titanate zirconate (PZT) film, barium strontium titanate (BST) film and the like which have a high dielectric constant and high step coverage have been developed and various filming methods relating these films have been examined. As to the raw materials of these films, Pb (DPM)2 (solid raw material) as a Pb source, Zr(OC(CH3)3)4 (liquid raw material) as a Zr source, Ti(OCH(CH3)2)4 (liquid raw material) as a Ti source, Ba(DPM)2 (solid raw material) as a Ba source and Sr(DPM)2 (solid raw material) as a Sr source are used.
Although as to solid raw materials among these raw materials, high purity raw materials can be obtained by keeping these solid raw materials at high temperatures to sublimate them and supplying the vaporized raw materials, it is very difficult to secure industrially sufficient supply amount. Therefore, these solid raw materials are used by dissolving each of these materials in an organic solvent such as tetrahydrofuran in general. Also, in a multicomponent type MOCVD process as aforementioned, the supply amount of each raw material is decreased. Hence an organic solvent is sometimes added also to the liquid raw material to control the supply amount for the purpose of supplying raw materials quantitatively with high accuracy.
Most of these liquid raw materials, solid raw materials and organic solvents used for these raw materials have high toxicity or have not been confirmed as to whether they are safe or not. It is therefore necessary to clean these materials before these materials are discharged to the air after they are used.
Such a harmful gas as is discharged from MOCVD processes has been usually purified by a wet method, dry method or combustion method.
For example, as the cleaning method using a wet method, a method has been practiced in which harmful gas containing an alkoxide is brought into contact with an aqueous solution containing an alkaline component to absorb and decompose the harmful gas thereby cleaning the gas.
As the cleaning method using a dry method, a method is known in which harmful gas containing an alkoxide is brought into contact with a cleaning agent obtained by impregnating a metal oxide using, as major components, copper oxide and manganese oxide with an alkali compound, e.g., potassium hydroxide to clean the gas (Japanese Patent Application Laid-Open No.6-327932). Also, a method is known in which harmful gas containing alkyl hydrides such as tert-butylarsine and tert-butylphosphine is brought into contact with a cleaning agent obtained by impregnating a metal oxide using, as major components, copper oxide and manganese oxide with a cobalt compound to clean the gas (Japanese Patent Application Laid-Open No. 7-60054).
Also, as the cleaning method using a combustion method, a cleaning method has been practiced in which harmful gas containing organic metal compounds is introduced into a flame of flammable gas, e.g., propane, and oxygen or air to burn the harmful gas.
Moreover, as a method for cleaning of the harmful gas containing organic metal compounds and organic solvents, a cleaning method is known in which the harmful gas containing harmful components is brought into contact with, for example, activated carbon or synthetic zeolite such as a molecular sieve to adsorb these harmful components.
However, the aforementioned cleaning method using the wet method has the drawback that the apparatus is large-sized and the aftertreatment of the used absorbing solution is troublesome.
The cleaning method using the dry method described in Japanese Patent Application Laid-Open No. 6-327932 has the drawback that methanol and ethanol produced by the cleaning of the alkoxide cannot be caught though metals contained in the alkoxide can be caught in the cleaning agent. The cleaning method using the dry method described in Japanese Patent Application Laid-Open No. 7-60054 has the drawback that butane and butene cannot be caught similarly to the above case.
The cleaning method using the combustion method has such a disadvantage that it requires high energy cost and a large amount of carbon dioxide is discharged since the state of burning must be maintained also during stand-by time when the harmful gas is not treated.
Moreover, the method for cleaning of the harmful gas containing organic metal compounds and organic solvents by using an adsorbent such as activated carbon or synthetic zeolite poses the problem that harmful components which have been once adsorbed dissociate depending upon treating conditions and the type of harmful component and the problem that aftertreatments such as incineration of the adsorbent after the cleaning of the harmful gas are troublesome. Further, when cyclic ethers such as tetrahydrofuran are contained as the harmful components, they produce peroxides in the presence of oxygen. Therefore, in the case of a large throughput, there is a fear that the aftertreatments are accompanied with risks.
Accordingly, an object of the present invention is to solve the aforementioned problems and to provide a method and apparatus for cleaning of the harmful gas, the method and the apparatus ensuring that harmful components can be purified in an efficient manner without discharging organic compounds and a large amount of carbon dioxide after the cleaning process and no aftertreatment is required when harmful gas discharged from, for example, semiconductor-manufacturing processes using organic metal compounds as reaction raw materials is purified.
The inventors of the present invention have conducted earnest studies to solve these problems and, as a result, found that harmful components can be efficiently converted into metal oxides, water and carbon dioxide to clean without discharging organic compounds and a large amount of carbon dioxide after the cleaning process and no aftertreatment is required by bringing the harmful gas discharged from reaction processes such as semiconductor-manufacturing processes using organic metal compounds as the reaction raw materials into contact with a catalyst obtained by carrying a noble metal on an inorganic support, a catalyst comprising of a metal oxide such as vanadium oxide, chromium oxide, manganese oxide, iron oxide, copper oxide, silver oxide cobalt oxide or nickel oxide or a catalyst obtained by carrying each of these metal oxides on an inorganic support to run catalytic combustion. The present invention was thus completed.
Accordingly the present invention resides in a method for cleaning of the harmful gas, the method comprising mixing harmful gas, discharged from reaction processes using organic metal compounds as the reaction raw materials, with oxygen or air and thereafter bringing the mixture into contact with a catalyst, obtained by carrying a noble metal on an inorganic support, at temperatures between 100xc2x0 C. and 800xc2x0 C. to clean the harmful gas.
Also, the present invention resides in a method for cleaning of the harmful gas, the method comprising mixing harmful gas, discharged from reaction processes using organic metal compounds as the reaction raw materials, with oxygen or air and thereafter bringing the mixture into contact with a catalyst comprising at least one metal oxide selected from vanadium oxide, chromium oxide, manganese oxide, iron oxide, copper oxide silver oxide, cobalt oxide and nickel oxide or a catalyst obtained by carrying the metal oxide on an inorganic support, at temperatures between 100xc2x0 C. and 800xc2x0 C. to clean the harmful gas.
Also, the present invention resides in an apparatus for cleaning of the harmful gas discharged from reaction processes using organic metal compounds as the reaction raw materials, the apparatus comprising a pipe for introducing harmful gas, a pipe for introducing oxygen or air, a cleaning column which is connected to said two introduction pipes and filled with a catalyst obtained by carrying a noble metal on an inorganic support, a means for heating the cleaning column and an exhaust pipe for discharging the purified gas discharged from the cleaning column.
Further, the present invention resides in an apparatus for cleaning of the harmful gas discharged from reaction processes using organic metal compounds as the reaction raw materials, the apparatus comprising a pipe for introducing harmful gas, a pipe for introducing oxygen or air, a cleaning column which is connected to said two introduction pipes and filled with a catalyst comprising at least one metal oxide selected from vanadium oxide, chromium oxide, manganese oxide, iron oxide, copper oxide silver oxide cobalt oxide and nickel oxide or with a catalyst obtained by carrying the metal oxide on an inorganic support, a means for heating the cleaning column and an exhaust pipe for discharging the cleaned gas discharged from the cleaning column.